Hydraulic control apparatus for vehicle power transmitting system having continuously variable transmission

A hydraulic control apparatus for a power transmitting system for an automotive vehicle having a continuously variable transmission which has an input and an output shaft, a pair of variable-diameter pulleys provided on the input and output shafts, respectively, a belt connecting the pulleys, and a first and a second hydraulic actuator which are respectively provided on said input and output shafts, for changing effective diameters of the pulleys, said apparatus including a two-position directional control valve having a first and a second position, for applying a first line pressure from a first pressure line to one of said first and second hydraulic actuators while applying a second line pressure from a second pressure line to the other of said hydraulic actuators, and a two-position flow control valve disposed between said directional control valve and said hydraulic actuators and whose duty cycle is controlled so as to control a rate of flow of a working fluid therethrough, whereby a speed ratio of said transmission is changed at a controlled rate, wherein the improvement comprises:

• a by-pass line connecting said second pressure line to said second hydraulic actuator;
• a one-way valve disposed in said by-pass line, for permitting a flow of the fluid therethrough in a direction from said second pressure line toward said second hydraulic actuator;
• and
• a flow restrictor disposed in said by-pass line, in parallel with said one-way valve.

A hydraulic control apparatus for a power transmitting system for an automotive vehicle having a continuously variable transmission which has a first and a second shaft, a pair of variable-diameter pulleys provided on the first and second shafts, respectively, a belt connecting the pulleys, and a pair of hydraulic actuators for changing effective diameters of the pulleys, said apparatus including means for applying a first line pressure and a second line pressure lower than said first line pressure to one and the other of said pair of hydraulic actuators, respectively, so as to control a speed ratio of said transmission, wherein the improvement comprises:

• a two-position directional control valve having a first and a second position for increasing and reducing the speed ratio of the transmission, respectively;
• a first solenoid coil for operating said directional control valve selectively to said first and second positions;
• a two-position flow control valve disposed between said directional control valve and said pair of hydraulic actuators, and having a first and a second position for changing the speed ratio of the transmission at respective two different rates;
• and
• a second solenoid coil for operating said flow control valve selectively to said first and second positions,
• said directional control valve having a drain port, a first line pressure port receiving said first line pressure, a second line pressure port receiving said second line pressure, four ports respectively connected to a first, a second, a third and a fourth connecting line, a spool having four lands for connecting said drain port and said first connecting line and connecting said first line pressure port and said third connecting line when said first solenoid coil is placed in one of energized and deenergized states thereof, and for connecting said first line pressure port and said second connecting line and connecting said second line pressure port and said fourth connecting line when said first solenoid coil is placed in the other of said energized and deenergized states,
• said flow control valve having a port communicating with said driving side actuator, a port communicating with a driven side actuator of said pair of hydraulic actuator which is provided on a driven one of said first and second shafts, four ports respectively connected to said first, second, third and fourth connecting lines, and a spool having three lands, for connecting said first connecting line and said driving side actuator and connecting said third connecting line and said driven side actuator when said second solenoid coil is placed in one of energized and deenergized states thereof, and for connecting said second connecting line and said driving side actuator and connecting said fourth connecting line and said driven side actuator when said second solenoid coil is placed in the other of said energized and deenergized states.

A hydraulic control apparatus for a power transmitting system for an automotive vehicle having a continuously variable transmission, hydraulic actuator means for controlling a speed ratio of the transmission, and a two-position flow control valve connected to said hydraulic actuator means, for regulating a rate of flow of a working fluid therethrough so as to control a rate of change in said speed ratio, said flow control valve having an open and a closed position for respectively selecting a first rapid and a second slow shifting mode in which the speed ratio of the transmission is rapidly and slowly changed, respectively, a duty cycle of said flow control valve being controlled so as to provide a third medium-speed shifting mode in which the speed ratio is changed at a continuously variable rate intermediate between rates of change in said first and second shifting modes, the speed ratio of the transmission being controlled in a selected one of at least two of said first, second and third shifting modes, so that a control error associated with said speed ratio is zeroed, wherein the improvement comprises:

• means for determining said control error;
• means for determining a duty cycle at which said flow control valve is operated so as to zero the detected control error;
• means for determining at least one boundary duty cycle value each substantially corresponding to a boundary between a controllable range and a non-controllable range of the rate of flow of the fluid through said flow control valve, said rate of flow of the fluid effectively varying with the duty cycle of the flow control valve over said controllable range, and not effectively varying with the duty cycle within said non-controllable range;
• and
• mode selecting means for selecting said one of at least two of said first, second and third shifting modes, by comparing the determined duty cycle with said at least one boundary duty cycle value.